Polyarylenes, especially polyphenylenes, exhibit some outstanding performance properties, including exceptionally high strength, stiffness, hardness, scratch resistance and dimensional stability. Unfortunately, polyarylenes have some limitations in toughness-related properties, in particular in terms of impact resistance and elongation properties. They have also limitations in melt processability due to their high viscosities, and tend to be anisotropic when melt fabricated under high shear such as during injection molding. Also, they have some limitations in chemical resistance. Also, they have some limitations in thermal resistance, which may cause some undesirable outgassing (weight loss) when submitted at very high temperature (380° C. or so).
Poly(aryl ether ketone)s, especially polyetheretherketones, exhibit also some outstanding properties, including exceptionally high melting point, excellent chemical resistance (including environmental stress cracking resistance) and excellent thermal stability. They have also high strength, stiffness, although somewhat lower than that of polyarylenes, and very good elongation properties. On the other hand, like polyarylenes, they have some limitations in terms of impact resistance.
Polymer blends have been widely taught and employed in the art. As broad as this statement may be, the blending of polymers remains an empirical art and the selection of polymers for a blend giving special properties is, in the main, an Edisonian-like choice. Certain attributes of polymer blends are more unique than others. The more unique attributes when found in a blend tend to be unanticipated properties. According to Zoller and Hoehn, Journal of Polymer Science, Polymer Physics Edition, vol. 20, pp. 1385-1397 (1982): “Blending of polymers is a useful technique to obtain properties in thermoplastic materials not readily achieved in a single polymer. Virtually all technologically important properties can be improved in this way, some of the more important ones being flow properties, mechanical properties (especially impact strength), thermal stability, and price ( . . . ). Ultimately, the goal of such modeling and correlation studies should be the prediction of blend properties from the properties of the pure components alone. We are certainly very far from achieving this goal.”
In the field of miscibility or compatibility of polymer blends, the art has found predictability to be unattainable, even though considerable work on the matter has been done. According to authorities, “It is well known that, regarding the mixing of thermoplastic polymers, incompatibility is the rule and miscibility and even partial miscibility is the exception. Since most thermoplastic polymers are immiscible in other thermoplastic polymers, the discovery of a homogeneous mixture or partially miscible mixture of two or more thermoplastic polymers is, indeed, inherently unpredictable with any degree of certainty, for example, see P. J. Flory, Principles of Polymer Chemistry, Cornell University Press, 1953, Chapter 13, page 555.”
U.S. Pat. No. 5,654,392 describes a class of polyphenylene polymers with phenylene units comprising a solubilizing side group which, because of this side group, are taught to help somehow in overcoming the problem of blending the rigid-rod and flexible components into a stable homogeneous phase (see col. 2, 1. 60-63). Per US'392, the rigid-rod polymers can be blended with thermoplastics, thermosets, liquid crystalline polymers (LCP's), rubbers, elastomers, or any natural or synthetic polymeric material (col. 4, 1. 16-20); US'392 keeps silent about the miscibility and compatibility of the polymers of such blends. It is of interest to note that, per US'392, only polymer blends containing a low amount of polyphenylene (at most 10 wt. %) with certain specific polymers could be prepared by a melt process [with polybutylene (example 23), nylon-6 (example 24), polystyrene and PPO (examples 24 and 25), polyethylene and polypropylene (example 25)], while blends comprising a higher amount of polyphenylene were prepared by solution mixing [blends with polystyrene (example 26) and polycarbonate (example 27)]; this suggests that the polymers involved in such blends have a very poor reciprocal miscibility/compatibility, or even are completely immiscible/incompatible, as many other couple of polymers are.
Example 13 of the same patent is a prophetic description (as evidenced by the use of the present tense and the absence of detailed operating conditions) of a pultrusion process involving a polyetheretherketone (PEEK) at molten state and fibers of a rigid-rod polyparaphenylene with a solubilizing group of high molecular weight, namely a poly 1,4-(4′-phenoxybenzoylphenylene). Accordingly, a fiber tow composed of the polyparaphephenylene fibers is continuously pulled through a PEEK melt and co-extruded through a die to form ribbed panels, which can be viewed as a composite material consisting of, as separate interconnected parts, essentially parallel polyphenylene fibers interconnected by a PEEK matrix so as to form a unified whole. In a pultrusion process, it is mandatory to preserve the fibrous nature of the fibers, so as to obtain a material with desirable properties, in particular a high modulus and strength; that the fibrous nature of the fiber is preserved in this prophetic example, is confirmed by the ribbed attribute of the panels (the ribs are deemed to be polyphenylene fibers), and also by the general teachings of US'392 about the pultrusion of polyphenylene fibers with thermoplastics (of undefined nature), from col. 21, 1. 54 to col. 22, 1. 3: “Related to extrusion is pultrusion, wherein a fiber reinforcement is continuously added to an extruded polymer. ( . . . ) the polymers of the present invention may be used as the fiber for pultrusion of a thermoplastic having a lower processing temperature. ( . . . ) lower cost thermoplastics having moderate moduli and strength can be formed into composites with high moduli and strength by the incorporation of rigid-rod or segmented rigid-rod polyphenylene fibers. Such a composite is unique in that the reinforcing fibers are themselves thermoplastic and further processing at temperatures above the fiber Tg will result in novel structures as the fibers physically and/or chemically mix with the matrix.” Back to example 13 specifically, by giving credit to a pultrusion process comprising which requires contacting, during a significant amount of time, polyphenylene fibers (which have a Tg as low as about 160° C.) with molten PEEK (PEEK at a temperature above about 340° C.) without affecting the fibrous nature of the polyphenylene fibers, US'392 gives thereby credit to the incompatibility and the immiscibility of polyphenylene also with PEEK, discarding thereby the skilled person from mixing a polyphenylene in a form other than fibers with PEEK in a significant amount so as to obtain a valuable blend, since, in such a case, the expectation would be great to obtain an unstable physical blend, highly subject to phase separation.
There remains a strong need for materials offering a superior balance of properties, including part or all of the following ones:                very high strength;        very high stiffness;        good elongation properties;        good melt processability (in particular, good injection moldability);        high chemical resistance;        outstanding thermal resistance [capable of inhibiting undesirable outgassing even when the material is submitted at very high temperature (380° C. or so)], desirably as high as that neat poly(aryl ether ketone); and        outstanding impact resistance, as possibly characterized by a standard no-notch IZOD test (ASTM D-4810), desirably higher than that of neat polyarylene and neat poly(aryl ether ketone).        